org.apache.hadoop.mapreduce.lib.join.ResetableIterator Maven / Gradle / Ivy
/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.mapreduce.lib.join;
import java.io.IOException;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.io.Writable;
/**
* This defines an interface to a stateful Iterator that can replay elements
* added to it directly.
* Note that this does not extend {@link java.util.Iterator}.
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
public interface ResetableIterator {
public static class EMPTY
implements ResetableIterator {
public boolean hasNext() { return false; }
public void reset() { }
public void close() throws IOException { }
public void clear() { }
public boolean next(U val) throws IOException {
return false;
}
public boolean replay(U val) throws IOException {
return false;
}
public void add(U item) throws IOException {
throw new UnsupportedOperationException();
}
}
/**
* True if a call to next may return a value. This is permitted false
* positives, but not false negatives.
*/
public boolean hasNext();
/**
* Assign next value to actual.
* It is required that elements added to a ResetableIterator be returned in
* the same order after a call to {@link #reset} (FIFO).
*
* Note that a call to this may fail for nested joins (i.e. more elements
* available, but none satisfying the constraints of the join)
*/
public boolean next(T val) throws IOException;
/**
* Assign last value returned to actual.
*/
public boolean replay(T val) throws IOException;
/**
* Set iterator to return to the start of its range. Must be called after
* calling {@link #add} to avoid a ConcurrentModificationException.
*/
public void reset();
/**
* Add an element to the collection of elements to iterate over.
*/
public void add(T item) throws IOException;
/**
* Close datasources and release resources. Calling methods on the iterator
* after calling close has undefined behavior.
*/
// XXX is this necessary?
public void close() throws IOException;
/**
* Close datasources, but do not release internal resources. Calling this
* method should permit the object to be reused with a different datasource.
*/
public void clear();
}